Malcolm Fairbairn
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COSMO 2013 Dark Matter Overview
Dec. 1-8, 2010
• Reminder – Why we think Dark Matter exists
• Indirect Detection of WIMPs
• Direct Detection of WIMPs
• Some Particle Models of WIMPs which are
still healthy in September 2013
Program
“I have a good idea every two years. Give me a topic, I will give you the idea!”
Fritz Zwicky Coma Cluster 1933
velocity of galaxies in the cluster is too large for the visible mass of the cluster
+
Wimps Work !
(at least for the dark matter bit)
Right amount of dark matter if dark matter mass 100 MeV < M < 100 TeV
We know that WIMP self annihilation
cross section has to be 3x10-26cm3s-1
Rate of self-annihilation of Dark Matter
We think we might know this
But how well do we know this
at the Galactic Centre?
And we have some ideas about this
Navarro et al 0810.1522
Simulations show halos denser in middle.
http://www.mpa-garching.mpg.de/aquarius/
Aquarius Simulations
Springel et al.
Comparison of
actual flux
with DM ann.
flux
Same Vertical
scale
g=1.2
g=1.6-1.7 The Galactic Centre
Coincidence
g = - d ln r / d ln r
Has Fermi detected
dark matter
annihilation at the
galactic centre?
Hooper and Goodenough.
arXiv:1010.2752
Boyarsky et al 1012.5839 Chernyakova et al. 1009.2630
Hooper+Goodenough purported DM spectrum
Alternative explanation for spectrum
Boyarsky et al 1012.5839 Chernyakova et al. 1009.2630
Chernyakova et al. purported proton induced spectrum
Alternative explanation for spectrum
Difference between scenarios may be
apparent using radio synchrotron,
situation unclear as yet
Fermi Analysis
Looking specifically
for Lines (Weniger 1204.2797)
Choose only those
pixels that will
together maximise
the overall signal to
noise ratio.
This choice is
based upon known
sources and differs
for each assumed
halo model.
Possible Evidence
for 130 GeV Dark
Matter
Annihilation Line?
4.6s or 3.3s when
taking into account
“look elsewhere” effect
Test statistic TS follows nice Poisson distribution
when applied to random data where you don’t
expect signal.
Repeated baryonic
contraction and
shocking reduces
central density of
dark matter.
If correct, bad for
indirect detection
signals.
arXiv:1202.0554
GENERAL NEW
PROBLEM FOR
INDIRECT
SEARCHES?
What can Inner Density Profile
of dSph galaxies tell us?
• Expected WIMP annihilation signal
• Is dark matter self interacting?
• Is dark matter warm/hot-cold/mixed/decaying
BORING HEALTH WARNING:- Gastrophysical effects can affect inner densities as
well as sexy new physics
Fermi constraints on gamma ray emission from Dwarf Spheroidals
However, this makes assumptions about the density
distribution that many people question. arXiv:1108.3546
Tangential
Velocity
Dispersion
Radial
Velocity
Dispersion
Can obtain this by fitting data
Cannot observe this directly for stars so free parameter
How do you work out how much
DM in Dwarf Spheroidals?
Use the Jeans equation and the line of sight stellar dispersion
Scenes from
Spherical/triaxial
Working Group at the
Gaia Challenge
University of Surrrey,
two weeks ago
New Method to Constraint Density of Dwarf Spheroidals
MF with Tom Richardson
Recovering test data
Red lines are
actual values
With and Without 4th
order information (Kurtosis)
G = d ln M / d ln r
Richardson and Fairbairn 2013
DOESN’T ALWAYS WORK SO WELL… YET
(see Tom’s Talk)
Branching ratio into e+e-
Thermally averaged self annihilation cross section at freeze-out
Thermally averaged self annihilation cross section today
Expected local density (0.3 GeV cm-3)
Actual local density
Possible origins of the Boost Factor
This enhancement not thought to be
large enough, see e.g. Pieiri, Lavalle,
Bertone and Branchini 0908.0195
Sommerfeld Enhancement
S-channel annihilations
P-channel annihilations
Need something else to enhance the cross section. If
Then dark matter particles are pulled together by exchange of W,Z bosons, enhancing annihilation by
Sommerfeld Enhancement
In general, we can consider a much lighter GeV boson, weakly coupled (Arkani-Hamed & Weiner 0810.0713)
Also DM annihilates through boson – muon final states! (no helicity supression)
However, since cross section goes like 1/v, forms problems for first structures formed (Kamionkowski and Profumo)
Sommerfeld Enhancement
In general, we can consider a much lighter GeV boson, weakly coupled (Arkani-Hamed & Weiner 0810.0713)
Also DM annihilates through boson – muon final states! (no helicity supression)
However, since cross section goes like 1/v, forms problems for first structures formed (Kamionkowski and Profumo)
i.e. the poor guy
who’s flight got
cancelled
Possible astrophysical origin of electrons/positrons 10 GeV – 10 TeV
SNR - Secondary Pulsars - Primary
Where are we now?
HOWEVER, 3% anisotropy still larger than that expected
from single pulsar, Linden and Profumo 1304.1791
SLIDE
STOLEN
FROM
AMS
WEBSITE
INDIRECT DETECTION:-
CONCLUSIONS
• Hints from galactic centre of low mass WIMPs.
• Other astrophysical explanations exist.
•Hints from galactic centre of gamma ray delta function.
• Understanding the density profile of Dwarf Spheroidals is important.
• Anomalous Positron and Electron flux might be a signal, might not.
An Aside – Self Interacting Dark Matter
1. Theories with Sommerfeld Enhancement contain
exchange boson leading to inter-DM force
2. Missing Satellites Problem (not enough dSph)
3. Core vs. Cusp Problem (dSph “cored not cuspy”)
4. Too Big to Fail Problem (Biggest dSph not as big as
CDM predictions)
MOTIVATIONS
2. and 3. can potentially be solved with baryons, 4. with baryons and
bad estimate for Milky Way Mass and 1. could just be plain wrong.
NEED TO TEST IT
An Aside – Self Interacting Dark Matter
For a potential
You expect the perturbative cross section (easy to work with)
However for real astrophysical systems, things can get non-perturbative, need to use
classical expressions from fitting numerical modelling of individual classical scattering in
potentials
Also many resonant effects (see e.g. Zurek 1302.3898)
An Aside – Self Interacting Dark Matter
Besides these difficulties, people are trying to constrain such
models using objects such as the Bullet Cluster and
Elliptical Galaxy NGC-720
Typical constraints are currently ~ cm2/g
which is around 1012 times weak interaction
Spherical Sources of
Astrophysical Uncertainty
• Uncertain Density profile
• Uncertain mass of galaxy
• Spherical Baryonic contraction
• Non Maxwellian Velocities
• Lack of knowledge of velocity Anisotropy b(r)
• Uncertain solutions to Jeans Equation
Non-Spherical Sources of
Astrophysical Uncertainty
• Tidal Streams
• Substructure
• Dark Discs (density and/or velocity)
• Effect of Baryonic Disk
• Effect of Spiral Arms
• Lack of axial symmetry of Galaxy
Let’s just look at Uncertainties in Spherical Profile
Tangential
Velocity
Dispersion
Radial
Velocity
Dispersion
Solutions of Jeans Equations
Can obtain this by fitting data
Cannot observe this so cannot be fitted
Fitting Galactic Parameters
Use Observed Baryonic Profile and Einasto Profile for Dark matter
Fit:-
• rotation of galactic disk
• local rotation and derivative
• Motion of distant blue stars
• Motion of Milky Way Satellites
Fairbairn, Douce and Swift 2012 (following Catena and Ullio)
Prediction for Velocity Dispersion
Fairbairn,
Douce and
Swift 2012
Then have to solve Jeans equation in this potential
• These Astrophysical issues affect different
experiments in different ways.
• Spherical Uncertainties much worse at low mass.
• Need a significant detection at multiple detectors
to 1) get a signal and 2) measure the mass
LUX- ZEPLIN 9 Tons
The UK forum for direct dark matter searches
“The DMUK Institute Board has decided to choose LUX-ZEPLIN as the UK direct dark matter project for a capital funding proposal to STFC in 2013/14. The current UK groups (Imperial, Edinburgh, UCL, RAL) already on LZ will be strengthened by Kraus and his group from Oxford and Kudryavtsev from Sheffield joining LZ. This is a decisive step in the implementation of the STFC Science Board Dark Matter Sub-Group Strategy for Dark Matter.”
Constrained Minimal Supersymmetric
Standard Model
All sfermion masses equal at GUT scale
All gaugino masses equal at GUT scale
Reduced to 5 free parameters
Superpartners of neutral gauge and higgs bosons mix into four
majorana neutralinos which make good WIMP candidate
Is Neutralino Dark Matter Still OK?
Higgs too
light
Stau lighter than neutralino
No EW breaking min. tan b=51
Stolen from Oliver Buchmuller talk at Dark Attack
(SUSY no-show, 125/6
GeV Higgs & XENON100)
Changing Direct Detection Predictions
Phenomenological Minimal Supersymmetric Standard Model PMSSM
See e.g.
Boehm, Dev,
Mazumdar &
Pukartas 2013
Fine tuning is sensitivity of
(observed) Z-mass to small
changes in parameters
Fits in PMSSM
Low mass DM Boehm, Dev,
Mazumdar &
Pukartas 2013
Higher mass DM Grothaus, Lindner and
Yakanishi 2012
Higgs Portal Dark Matter
Simply another particle which couples to the Standard model
through the Higgs
Scalar dark matter Standard model Higgs Field
V. Silveira, A. Zee, Phys. Lett. B161, 136 (1985);
J. McDonald, Phys. Rev. D50 (1994) 3637-3649;
C. P. Burgess, M. Pospelov, T. ter Veldhuis, Nucl. Phys. B619 (2001) 709-728 [hep-ph/0011335]
Particle Candidates:- Conclusion
• As the LHC probes the electroweak scale, all WIMP
models are facing tighter constraints as one would
expect
• The simplest models of SUSY are under severe
pressure, but it will be some time before SUSY itself can
be ruled out as the origin of dark matter.
• Many more much simpler models are being studied in
the light of the new data which will also face (welcome)
pressure in the next few years.
CONCLUSIONS
Indirect, Direct and Collider experiments are severely
constraining the parameter space of WIMP models.
THIS IS GOOD!!!
With more running of the LHC and the next generation of
direct detection experiments, SEVERE constraints will be
placed on MOST WIMP scenarios.
Astrophysicists and Particle Physicists are working
together in new ways to constrain the nature of dark
matter, be it WIMPs or otherwise
Next few years will be a VERY exciting time for
dark matter physics.
One Example of a working Higgs Portal model
Fairbairn and Hogan 2013
Additional scalar field s coupled only through the Higgs:-
S is coupled to a singlet Dirac Fermion which is dark matter
Leads to two mass eigenstates and a mixing angle
Constrained by experiment
One Example of a working Higgs Portal model
(Ellis and You ’13,
Falkowski, Riva and Urbino, ‘13)
Similar analogous constraints for the decay of h2.
Still plenty of room though…
Monojets at the LHC
Imagine some purely phenomenological contact interactions for
coupling between dark matter and standard model particles
Bai, Fox and Harnik arXiv:10053797